How to Retry a workflow step Programatically?

Hi All,

whenever we'll get a exception in a particular process step, there will be a option called "retry" instead of "complete"

if we select that retry option, the particular step will be re executed again

if there is no exception it will move to its next forward state

if there is still exception the workflow should be there in that process step nly

this thing i need to acheive programatically

Thanks!